1. Field of the Invention
The present invention relates generally to telecommunication networks, and more particularly to a system and method for evaluating and expressing availability of a telecommunication network.
2. Related Art
Among providers of telecommunication network services, the term "availability" refers to the proportion of time that a given customer will be able to use a particular service or connection. Annually observed empirical availability may be somewhat less than 100% due to simultaneous equipment failures, natural events, accidental damage, and the like.
The commonly accepted way of evaluating and expressing availability is described in ITU standards M2100 and G.826. When a network service provider quotes an availability figure to an existing or prospective customer, the provider identifies the types of links that will serve the customer, such as radio, cable, fiber, satellite, etc., and the length of each type of link. Then the provider multiplies these parameters by commonly agreed upon factors that rate the likelihood of failure for a given type and length of a communications link. Thus, the service provider finally arrives at an estimated availability percentage that takes into account equipment failures and cable damage or link outages. This commonly used method of determining availability implies that a spare path is always available without any restrictions or conditions for backup procedures.
In practice, there is another significant factor that can degrade the actual availability experienced by a customer over a period of time. This additional factor is introduced as network maintenance personnel carry out repairs, retrofits, tests, add-ons, moves, and changes within the network that temporarily render some links unusable. Of course every effort is made to avoid interrupting a working link as this can be costly and troublesome for both the service provider and customer. Planned maintenance actions try to make judicious use of spare links that are otherwise used only in the event of failed network elements. Maintenance personnel will usually divert live traffic from a working link onto a spare link in order to perform actions on the working link. Sometimes a spare link itself may be disabled for a time as changes are made. A problem arises when a spare link is occupied or disabled at the same time when a random failure occurs in the network or a manual switchover is mistakenly triggered. This coincidence can cause interruption of service.
What is needed is a method for quantifying and expressing availability that takes into account the impact of maintenance actions by network personnel. More specifically, what is needed is a system and method for monitoring the frequency and duration of maintenance actions within an actual network over a period of time, characterizing the average impact of such actions, and, upon request, deriving an empirically-based availability estimate applicable to a specific customer or portion of the network.